Dr Koppens conducted his PhD research in Delft under the supervision of Leo Kouwenhoven and Lieven Vandersypen, one of the top scientists working on quantum information processing with spins. In recognition of this achievement, he was awarded the prestigious Huygens prize for his ground-breaking work on quantum technologies”. After his PhD, Dr Koppens obtained a postdoctoral position at Harvard with a prestigious IQC fellowship.

Light propagating along the surface of graphene (plasmons), visualised by a scanning near-field microscope.

Koppens is a world leading researcher on graphene nano-optoelectronics and nano- optics. His diverse research activities have led to high-impact publications and to new research directions followed by many other researchers. One example is the first realization of an integrated quantum plasmonic circuit with on-chip detection [Nature Physics 5, 475 (2009)]. This hybrid quantum nano-optoelectronic system, interfacing single photons, plasmons and electrical plasmon detectors, has enabled electrical detection of surface plasmons emitted by a single quantum dot.

Koppens’ contributions to the graphene opto-electronics field have laid the foundation for two novel subfields: graphene-based hybrid systems and graphene nano-photonics (surface plasmonics). Koppens’ group demonstrated the first highly-sensitive graphene-based photodetection for infrared frequencies [Nature Nanotechnology 7, 363 (2012)], using a hybrid device based on graphene and semiconductor nanoparticles, which exhibits a detection sensitivity 10 million times higher than former existing graphene photodetectors. This landmark advance has opened pathways for novel infrared detectors, flexible detectors for wearables etc.

Graphene, a material with many fascinating properties, exhibits extraordinary optical behaviour. One specific outstanding feature is the so-called surface plasmons, wave-like excitations that were predicted to exist in the sea of conduction electrons of graphene. The wavelength of graphene plasmons is 100 to 150 times smaller than the wavelength of light, enabling very strong light confinement as well as slow light, relevant for a plethora of applications such as sensors and opto-electronics.

Graphene surface plasmons are tunable by voltages and can be converted into electrical signals, providing a unique platform for merging nano-photonics and nano-electronics. Dr Koppens was one of the pioneers in this field of graphene plasmonics. He recognized the potential of graphene surface plasmons and published pioneering work (e.g. Nano Lett. 11, 3370 (2011)) establishing new directions for graphene optics and opto-electronics. Shortly after, his long sought after goal was achieved: the first observation of propagating graphene surface plasmons and active electrical control of graphene-based plasmonic cavities [Nature 487, 77 (2012)]. The experiments revealed that graphene is an excellent host for guiding, confining and electrical manipulation of light at nanoscale dimensions. Recently, the group led by Koppens has realized significant progress in the field of graphene plasmonics by exploiting graphene-boron nitride heterostructures [Nature Materials 14, 425 (2015)] and showing high- quality factors for highly-confined plasmons and antenna-based plasmon launching [Science 344, 1369 (2014)].

They have also performed pioneering work investigating graphene as a promising material for light harvesting and photodetection. This includes the first observation of highly efficient carrier interactions after photo-excitation in monolayer graphene and the quantification of the conversion efficiency of light into the electronic degree of freedom [Nature Physics 9, 248 (2013)]. The field of carrier-carrier and light-carrier interactions in graphene is very rich, as it involves many-body interactions and ultra-fast timescales. The strong carrier- carrier interactions were recently observed and monitored with record-high time resolution [Nature Nanotechnology 190, 437 (2015)].